The present invention relates to a system for detecting an angular position of crankshaft relative to a specific cylinder of an engine for a motor vehicle, and more particularly to a system for discriminating a specific cylinder and for controlling the engine in accordance with the discriminated cylinder.
Heretofore, various systems for controlling the ignition timing for an internal combustion engine for a motor vehicle have been proposed.
Japanese Patent Application Laid-Open 60-27785 discloses a system in which a camshaft is provided with a cam timing pulley having projections which is securely mounted on a camshaft. A cam angle is detected by sensing the position of the projection with a photosensor, thereby detecting the top dead center on the compression stroke of a cylinder to be controlled. By detecting the cam position relative to the specific cylinder, other cam positions with respect to the other cylinders can be determined.
Japanese Patent Application No. 62-290227 discloses a system in which a sensor is mounted on a crankshaft of an engine for producing a reference crank signal in the form of a pulse and a sensor is mounted on a camshaft for producing a cam signal for detecting the top dead center of a cylinder, so that cylinders can be discriminated, thereby controlling the ignition timing of a corresponding cylinder.
In the former system, the camshaft is connected to the crankshaft by a timing belt so as to be rotated at half speed of the crankshaft. However, it may occur that the camshaft does not synchronize with the crankshaft during a period after the starting of the engine. Consequently, the system does not properly control the ignition timing to fail to start the engine. In the latter system, the crankshaft may not be in synchronism with the camshaft because of tolerances in manufacturing processes. It is necessary to provide a spare time between the reference crank signal and the cylinder discriminating signal.
If a magnetic pickup is used as sensing means, the pulse width and/or the number of the pulses must be expanded for producing an output signal having a sufficient voltage. However, it is difficult to increase the number of pulses in multiple-cylinder engines.